Weight-loss weigh feeders are used to meter dry and liquid ingredients, at specific feed rates, either on a continuous or batch basis, into a wide range of processes. In many applications, weight-loss weigh feeders can be used to proportion various ingredients that comprise a particular formulation (e.g, foods, plastics, chemicals, pharmaceuticals, etc.).
Generally, weight-loss weigh feeders include a vessel (e.g., a hopper or tank appropriately designed and sized for specific ingredients and/or applications) mounted onto a weighing system (e.g., a scale) where product discharge is regulated based on a desired discharge or feed rate (i.e., weight output vs. time).
Typically, product is discharged out of the vessel by applying a metering device. The loss of weight, as sensed by the weighing system, can be transmitted to the feeder's controller and calculated into a feed rate (e.g., pounds or tons per minute or hour). The controller then can compare the calculated rate of discharge to a desired (set) discharge rate and simultaneously modulate the output of the weigh feeder's metering device to maintain the desired (set) rate.
Weight-loss weigh feeders require the weigh vessel be periodically refilled with product. In some applications, the weight-loss weigh feeder also may need to operate under the presence of dry air, or a gas purge (e.g., nitrogen, helium, argon) to prevent the material being handled from being exposed to potentially adverse reactants, such as ambient air. Generally, these applications require internal areas of the weight-loss weigh feeder to operate in the presence of some pressurized inert gas that forces out ambient air from within the feeder, and/or precludes ambient air from entering the feeder. The introduction of internal pressure in the vessel (whether constant or fluctuating), however, can create forces upon the weighing system that adversely affect accurate performance during normal operation.